Dasyatis colarensis, Hugo Ricardo Secioso Santos, Ulisses Leite Gomes & Patricia Charvet-Almeida, 2004

Hugo Ricardo Secioso Santos, Ulisses Leite Gomes & Patricia Charvet-Almeida, 2004, A new species of whiptail stingray of the genus Dasyatis Rafinesque, 1810 from the Southwestern Atlantic Ocean (Chondrichthyes: Myliobatiformes: Dasyatidae)., Zootaxa 492, pp. 1-12 : 4-10

Dasyatis colarensis n. sp.

(Figures 1-6, Tables I and II)

Holotype - MNRJ 25179, mature male, 2070 mm TL, 630 mm DW, Marajó Bay, close to Colares Island, district of Colares, Pará State, Brazil, 00° 54’ 39’’ S, 48° 17’21’’ W, approximately 6 meters deep, water temperature 28.6°C, salinity 4 ppt, collector, P. Charvet-Almeida, 05/ XII/ 2001.

Paratypes - UERJ 2006, subadult male, 1810 mm TL, 530 mm DW, Marajó Bay, close to Colares Islands, district of Colares, Pará State, Brazil, collector P. CharvetAlmeida, 05/ XI/ 2003 ; MCP 34811, juvenile male, 1260 mm TL, 330 mm DW, same locality and collector as the other paratype, 04 / XI / 2003 .

Diagnosis

Dasyatis colarensis n. sp. is distinguished by the combination of the following characters: a diamond-shaped (rhomboid) disc and an elongate snout (preorbital distance ranging from 35.7 to 37.7 % in DW); presence of a dark and well defined band outlining the lower lips; row of small tubercles along midline of disc from shoulder region to base of tail, tubercles somewhat randomly distributed; posterior margins of pectoral fins uniformly rounded; triangular-shaped pelvic fins with posterior margin almost straight or slightly sinuous, pelvic fin tips exceeding posterior margins of disc; dorsal caudal keel absent in the holotype, but vestigial in both paratypes.

Description

Proportional dimensions as percentages of DW and meristic data are given respectively in tables I and II.

Snout long (preorbital length 35.7 to 37.7 % of DW) and acutely pointed. Maximum anterior angle in front of spiracles (snout angle) about 95° to 100°. Anterior margins of disc slightly concave with posterior margins convex. Disc width about equal to disc length (from 100.7 to 103.3 %). Eyes small, horizontal eye diameter 18.9 to 24.2 % in interorbital width. Spiracles well developed (horizontal eye diameter 35.5 to 47.0% of spiracle length). Posterior margins of pectoral fins perfectly rounded.

Corners of nasal curtain rounded; nasal curtain with fringed posterior margin and with a median hiatus. Mouth arched, with a straight and dark band outlining the lower lips. Median portion of lower jaw (symphysial region) slightly concave. Teeth in a pavement pattern; cusps pointed and curved backwards in the holotype. Subadult specimen with teeth near symphysis almost pointed. Dental formulae: 43-45/45-60. Three to four papillae in transverse series on mouth floor. In the holotype, the central papilla is curved forward, the two lateral ones show a singular bifurcated tip (paratypes have no bifurcated papillae). Gill slit apertures sinuous.

Pelvic fins triangular, with posterior margin almost straight or slightly sinuous. Tip of pelvic fin sharp, exceeding the limits of the posterior margin of disc. Well developed claspers in the holotype (with residual traces of sperm at the moment of capture). Medial margin of clasper groove slightly serrated at the glans. Tail (which seems complete) more than twice disc width (209.6 to 296.3%). Dorsal caudal keel absent in holotype but present in both paratypes as a low vestigial keel. Ventral finfold not high, its maximum height less than one third of caudal diameter at sting level (from 22.2 to 28.5%).

Central upper surface of disc covered with small, widespread, and flattened tubercles in a band along midline from level of orbits to base of tail. Tubercles also on rostral, preorbital and interorbital regions. Margin of disc naked. Dorsal thorn counts: 6 to 9 nuchals, 1 to 2 scapulars, 2 to 3 suprascapulars on the left side and 1 to 3 on the right, 12 to 17 median dorsals, and 6 to 9 median caudals. Ventral finfold, pelvic fins, claspers and ventral surface of the disc smooth. Sting missing in holotype (probably removed, original groove present). Counts of lateral sting barbs: 42 (left) and 48 (right) in juvenile paratype, 69 (left) and 70 (right) in subadult specimen.

Coloration in life very similar to that in preservative. Dorsal surface of the disc light brown; ventral surface whitish-gray with margins of pectoral fins and posterior margins of pelvic fins darker. Anterior margin of pelvic fin whitish to yellowish. Claspers and caudal ventral finfold dark brown.

Etymology

The specific name was selected for the geographic location of holotype, from the proximities of Colares Island, district of Colares ( Pará State, Brazil).

Discussion

Dasyatis colarensis resembles the diamond shaped, long snouted Dasyatis species group of Compagno and Roberts (1982, 1984), Nishida and Nakaya (1990) and Rosenberger(2001). According to Rosenberger (2001), in the western Atlantic this species group is represented by Dasyatis geijskesi , D. guttata , and D. sabina , which have preorbital snout lengths exceeding 25% of DW. The other western Atlantic species of Dasyatis , D. americana , D. centroura , D. marianae , and D. say either have or lack diamond shaped discs but all have snouts that are less than 25% of disc width.

The shape of the disc, which is laterally rounded, promptly differentiates D. sabina from D. colarensis , which has angular pectoral fin edges. In D. sabina the horizontal eye diameter is more developed (53% to 88% of spiracle length), whereas in D. colarensis this proportion is 35.5 to 47.0 %. In D. sabina the upper surface of tail has a definite and high finfold, and the ventral finfold is larger than the caudal height. In D. colarensis the dorsal finfold is absent (holotype) or vestigial (paratypes) and the height of the ventral finfold does not reach one-half of tail. The snout of D. sabina is shorter than in D. colarensis ; horizontal eye diameter is 5.6 to 6.9% of preoral length in D. colarensis , and the preoral length is 34.8 to 36.7 % of DW. In D. sabina these percentages are, respectively, 14% to 22% and 27. 7 % to 26.4%.

D. colarensis resembles D. guttata in possessing a rough patch of small tubercles at the midline dorsal area and on the elongated snout. The dorsal patch of tubercles of the disc in mature D. guttata forms a more or less defined band, while in D. colarensis the dorsal tubercles present a random arrangement. The snout of D. guttata is shorter than in D. colarensis . The horizontal eye diameter is 10% to 39% in preoral length in D. guttata whereas in D. colarensis it is 5.6 to 6.9 %. In addition, the preoral length is 21.5 to 25.5% of DW in D. guttata , and 34.9% to 36.7% in D. colarensis . The posterior margins of pectoral fins are perfectly rounded in D. colarensis and angular in D. guttata . The posterior margins of the pelvic fins are rounded in D. guttata and pointed in D. colarensis .

Dasyatis geijskesi differs from D. colarensis in possessing a very long preorbital snout length (40 to 50% of DW vs. 35.7 to 37.7% in D. coloarensis ), very long prenasal snout length (37 to 45% of DW vs. 29.5 to 32.7%), very broad pelvic fins (38 to 42.9% of DW vs. 19.6 to 23.3%), and narrow pelvic fin base length (79.3 to 91.1% of internasal length vs. 119.2 to 124.2%).

With respect to Dasyatis from other regions, D. colarensis resembles D. zugei ( Mueller & Henle, 1841) from China, Pakistan, Indonesia and the Sea of Japan, D. navarrae (Steindachner, 1892) and D. bennetti ( Mueller & Henle, 1841) from southeast Asia, and D. acutirostra (Nishida and Nakaya, 1988) from the Sea of Japan and the East China Sea, in having an elongated snout which reaches more than 25% of disc length (Chen, 1948; Chu & Wen, 1982; Monkolprasit, 1984; Nishida & Nakaya, 1990).

The pale-edged stingray D. zugei and the blackish stingray D. navarrae differ from D. colarensis by presenting a well developed upper finfold in the former, and vestigial or absent finfold in the latter.

The frilltail stingray D. bennetti lacks a patch of tubercles on the back of the disc (present in D. colarensis ), its ventral finfold length is 60% to 67% of DW (37.3 to 51.5% in D. colarensis ), its preoral length ranges from 25.7% to 27.4% of DW (34.8 to 36.7% in D. colarensis ), its pelvic radials range from 21 to 24 (26 in D. colarensis ), and it has 119 pre-sting vertebral centra (127 in D. colarensis ).

The smalltooth stingray D. rudis possesses the entire dorsal surface of disc rough with minute and dense asperities and no middorsal row of spines ( D. colarensis presents small tubercles only at disc centre and a middorsal row of spines).

The sharpnose stingray D. acutirostra presents a ventral finfold length ranging from 15.0% to 22.9% of DW (37.3 to 51.5% in D. colarensis ), a preoral length ranging from 37.9% to 44.2% of DW (34.8 to 36.7% in D. colarensis ), lacks a dorsal patch of tubercles and suprascapular thorns (both present in D. colarensis ), and lacks oral papillae (three to four well developed papillae in D. colarensis ).